The volcano Pele erupts over the limb of Jupiter's moon Io in this composite image from the Galileo spacecraft.The plume rises about 200 miles (300 km) above the surface of Io, which is coated in sulfur compounds from hundreds of volcanoes. [NASA/JPL/USGS]

Jupiter’s moon Io looks like it has a bullseye painted on it — a bright red oval around a dark hourglass. It’s hundreds of miles across, and it’s remained in view for decades.

The “bullseye” is a ring of material from one of the hundreds of volcanoes that dot Io’s surface: Pele, which is named for the Hawaiian volcano goddess.

Pele is a pool of superhot lava filling a basin near the foot of a plateau. It’s about 20 miles wide — far bigger than any similar feature on Earth — and it’s fed by lava bubbling up from below.

This pool of molten rock can sometimes produce powerful eruptions, sending plumes of gas and volcanic ash up to 300 miles high. Over time, some of the material from the plumes is swept up by Jupiter’s magnetic field, forming a “doughnut” around the giant planet.

But much of the material falls back to the surface. It contains a lot of sulfur compounds, which form the red ring around Pele as they settle as far as 375 miles away.

Several spacecraft have studied Io over the last three decades, and they’ve all seen the ring. It’s constantly changing, though, as other volcanoes cover parts of it, or as Pele itself adds fresh deposits. Despite the changes, though, the ring is still Io’s most prominent feature — a bright red bullseye on a volcanic moon.

Io’s planet, Jupiter, is in great view tonight, a little to the right of the Moon as they rise in early evening. Jupiter looks like a dazzling star.

Script by Damond Benningfield, Copyright 2011

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